Class 3 Assignment: Introduction to Cartographic Principles + Thematic Mapping - Part I

WRI - Global Power Plant Database | https://datasets.wri.org/dataset/globalpowerplantdatabase

Concepts & Themes:

This week’s assignment will encompass the following concepts covered in Class 3 lecture & lab:

  • Cartographic principles

  • Reference Maps vs Thematic Maps

  • Nominal vs continuous data types

  • Thematic strategies (3): Dot Density, Categorical Symbolization & Proportional Symbolization

  • QGIS style layers

  • Map layout elements: scale bars, map insets, complex legends & labels

Assignment Preamble:

Class 1 and 2 assignments featured the production of two maps - a small scale simple populated places global map and a large scale NYC 311 public service map. In a way, both maps are reference maps and simple thematic maps: they both have a theme but their primary purpose is simply to show the location of each theme:

  • Where are the locations of populated places?
  • Where are the location of 311 public service records in NYC based on one particular theme?

The Class 3 mapping assignment will build on the first two maps, but with significantly more emphasis on the thematic dimension of the mapped data - the distribution of global power generation across both type (nominal) and generation capacity in megawatts (quantitative). This week’s mapping will also focus on map layout adding in both a scale bar and an inset map element.

The dataset utilized in this mapping will be the Global Power Plant Database v1.3.0 which is open and accessible at WRI.

Global Power Plant Database v1.3.0

This dataset format is .csv with lat/lon coordinates; we will rely on Class 2 fundamentals to import and initially map this dataset. A polygon reference layer will be added - countries, states or regions - and proportional as well as categorical symbolization will be developed for the power plants. Finally, map layout elements - particularly a simple scale bar and inset map - will round out the assignment deliverable.

A synopsis of the assignment steps:

  • import data.
  • categorically symbolize data
  • proportionally symbolize data
  • create legend
  • create scale bar
  • create inset map
  • create other map elements - title & map author/source tag
  • finalize map layout design, export as PDF, PNG or TIFF and submit assignment to Canvas Class 3.

Assignment Steps:

Project setup & data organization:

Note general concepts covered in lecture and lab:

  1. Subselecting features

  2. Symbolizing nominal data

  3. Proportional symbolization of continuous quantitative data

  4. Scale bar production

  5. Map inset production

  6. Spatial bookmarks

  7. Labeling in QGIS (lab)

  8. Style layers in QGIS (lab)

  9. Dot density mapping (lab)

  • Step 1, Download the assignment data folder (unzip the .zip). Navigate QGIS to an Assignment.3 folder that you create; place and unzip the data folder and created a new .qgs assignment 3 project - all within the Assignment.3 directory. In the assignment data folder, find the following data sources:

Assignment Data Directory

  • Class 3 Assignment Data

    • global.regions = world boundary polygon featuring UN world regions schema
    • ne_10m_admin_0_countries_lakes = Natural Earth world countries polygon feature
    • US_States = US states boundaries clipped to shoreline polygon feature
    • globalpowerplantdatabasev120 = WRI Global Power Plant Database

Note: as of June 2021, the WRI Global Power Plant Database has been updated and can be accessed HERE. Replace the globalpowerplantdatabasev120 in the assignment folder with this updated global_power_plant_database_v_1_3.

  • As noted above, there are 3 polygon features in addition to the .csv for the power plants. These features are located in the respective folders outside globalpowerplantdatabasev120:

Assignment Data Directory

  • The three polygon features represent different recognized geographies at different scales. First, the UN regions schema is the smallest of the 3 scales; Natural Earth countries the second smallest; and US States represents the largest scale geography. You will pick one of these geographies that interests you most. For instance, the following 3 declarative sentences offer 3 example scale options to use for assignment 3:

    • Powerplants within the Western Asia Region
    • Powerplants within the country of Ukraine
    • Powerplants within the US state of Florida

Polygon Features for 3 scales that can be utilized in Assignment 3

  • Step 2, for demonstartion purposes, the assignment guide will utilize the country of Ukraine as the project Area of Interest. To select an Area of Interest from 1 of the 3 geographic scale levels, first label the respective feature polygon layer as follows:

right-click feature layer > Properties > Labels > Single Label

  • With Single Label option selected, utilize the dropdown to point to the attribute table field that best repents the name or ID of the geographic features in the polygon layer:

Single Label Tool Dialog

  • The result will place a label per polygon. This is helpful in navigating and developing your geographic choice:

Labels Result

  • Next, make a subselection within the attribute table to select the feature - in this case Ukraine. Here will will make a simple SQL (Structured Query Language) declaration to select Ukraine (replace Ukraine with your choice geography):

right-click > Open Attribute Table:

Open Attribute Table

> Select by Expression:

SQL Tool Button

*>Fields and Values > NAME:

SQL Expression Setup - Search

Note: keep in mind that the exact SQL expression that you use for your own query will be structured differently.

  • Record the SQL expression and Select at the lower right of the tool dialog box:

SQL Expression Setup

Select Features based on SQL Expression

  • The result will be 1 selected record in the attribute table for Ukraine, and a yellow selection within the Map Canvas:

Selected Results will be Highlighted on Map

  • Export this selection, making sure to export just the selection alone. Save this record as .shp into the assignment data folder:

Export a Selection

  • Step 3, with the selected geography complete, move along to creating project Spatial Bookmarks. These will be used to ‘keep track’ of both scale and position of various map ‘locations’ within one .qgs project. The first will be large scale, centered on Ukraine; and a second will be a regional scale and position to capture the geographic context of Ukraine relative to its postion within the European continent:

View > New Spatial Bookmark:

Spatial Bookmark Setup

  • In order to access and view created Spatial Bookmarks:

View > Show Spatial Bookmarks:

Spatial Bookmark Access

  • From the Browser Panel, the bookmarks are available to toggle on/off:

Spatial Bookmark Access

  • Step 4, next read in the Delimited Text .csv for the power plant locations:

Delimited Text Selector

  • Step 5, next Select by Location those plants within your selected geography - in this case, Ukraine:

Select by Location

  • Next, populate the tool dialog as follows:

Select by Location

  • Like Select by Attributes, these results will be selected both in the attribute table and on the Map Canvas as highlighted features. Export these selected features using the Save Selected Features As option utilized previously. Name the results to distinguish that the theme is power plants within the target geography, i.e. power.plants.ukraine.shp:

Export Selected Features

Map symbolization:

  • Unlike assignments for class 1 and class 2 that stopped short of any thematic symbolization (resulting in a map similar to above - simple, one symbol points atop polygons), this assignment pushes further into the data attributes themselves to provide the map user with much more information beyond location alone. Here two thematic symbolizations will be provided. The first will be the size of the plant based on megawatt capacity (MW); and secondarily, the type of the plant based on primary fuel. This provides the user with 3 dimensions of data for the plants:

    • Location - (lat/lon)
    • Size - measured as MW capacity (capacity_mw)
    • Type - determination of primary fuel type (primary_fuel)

  • Utilize the steps below with the following video guide (click on image for video in new window) to develop the map symbolization:

Proportional + Categorical Symbolization- Part II

  • Component 1 - The Size Assistant:

right-click > Properties > Symbology (Simple Marker) > Size > Assistant (via dropdown):

Size Assistant

  • Within the Assistant tool, there are several methods and options available; this is discussed in the video as well.

Size Assistant Parameters

Note: experiment with all the option parameters to become familiar with this powerful tool. Also note that the default style in the current LTR is a nested proportional symbol.

  • Proportional symbol (size) result:

Proportional Symbols on Map

  • In addition to the Size Assistant, categorical symbolization can be completed via the standard classification option under layer properties:

right-click > Properties > Symbology > Categorized (top bar):

Populate the tool:

  • Value: primary_fuel

  • Symbol: simple circle

  • Color Ramp: Random colors

  • click Classify (lower left)

Categorized Symbols - In conjunction with the Size Assistant, activate Data-defined Size Legend, also covered in the video.

right-click > Properties > Symbology. Notice the Advanced tab, lower-right. Activate Data-defined Size Legend:

Data-defined Selector

  • In the resulting tool dialog, notice the two options. Choose either option:

Note: the Collapsed Legend option is very elegant and effective over the default Separate legend items.

Collapsed Legend

  • As the proportional symbolization of larger points may cluster and crowd out smaller point quantities, apply approximately 60% transparency to the primary layers, also covered in the video.

  • Properties > Symbology > click-on Symbol > decrease Opacity to approximately 50-60%:

Apply Transparency

Make sure to save the .qgs early in the visualization process before proceeding to the final layout.

Quantitative Proportionality + Categorized Symbology

  • With initial symbolization complete, create a new layout (Layout Toolbar > New Layout) and draw out a map instance. All preparation and layout components are covered in video guide.

  • Proportional & Categorical Symbolization:

Proportional + Categorical Symbolization- Part II

  • It is recommended to create the map scale bar and map inset map prior to finalizing the legend item. You will notice these elements are not covered in the main video guide, but they are covered in the videos below.

Map layout & Deliverable:

  • To development the final map design, utilize the diagram, map example PDFs and the video guides in the Video Guides section below.

  • Final map layout will include the following elements on either a 11x17" or 8.5x11" Landscape 300 DPI:

    1. Main map frame featuring a polygon selection (state, country or region) with symbolized power plant locations within the polygon boundary.
    2. A map title
    3. Legend representing both proportional (size) and categorical (color) symbolization for power plants
    4. Simple scale bar
    5. Inset map with extent locator

Note: if a PDF export is exhibiting a large file size, .png or .tiff are acceptable.

  • Utilize the following diagram and map example to strategize your own map layout design:

Assignment 3 Deliverable Example

Map Design Exceptions & Notes:

  • Attend to the export file size for this week’s assignments. QGIS has a tendency to produce very large PDF file sizes as with proportional symbolization. Anything over 20 mb should be save alternatively as .png or .tiff - both are acceptable to the Canvas submission endpoint for this week’s submission:

Export as Image Option

  • Proportional symbolization in QGIS version 3.14 and greater is more flexible than the previous LTR 3.10. Utilize the new, nested legend style for a cleaner, compressed look. In the current LTR, the option to ‘nest’ the proportionality symbols is readily available (see example below):

Compressed, Nested Proportion Legend Style

  • There is often a difference in stroke weight/appearance in map canvas vs map layout vs export when designing with proportional symbolization; each instance of the map design process may exhibit a slightly different stroke weight appearance. Typically, the stroke weight needs to be exaggerated slightly in the map canvas to avoid an underexposed final stroke weight in the map output. Below is an example of a light stroke weight that works fine in map layout and export; anything lighter than this may be difficult to see in the final map output:

Map Canvas vs. Map Layout Stroke Weights

Video Guides:

  • Understanding Map Scale:

map scale video

  • QGIS Scale Bar Development:

Scale Bar Development

  • Inset Map Development:

Inset Map Development